A comparison of 250-meter resolution MODIS Red/Green/Blue (RGB) true color (using Bands 1/4/3) and false color (using Bands 7/2/1) images from the SSEC MODIS Today site (above) showed the main portion of the surface oil slick in the northern Gulf of Mexico on 24 May 2010. This was Day 34 following the deadly explosion on the offshore oil rig Deepwater Horizon, and the damaged underwater wellhead continued to discharge more than 5,000 barrels of oil per day.

A day later, MODIS true color and false color images from 25 May 2010(below) continued to exhibit a distinct signature of the surface oil slick.

The clouds eventually cleared out enough to reveal portions of the oil slick (which remained off the coast of Louisiana following from the explosion and sinking of the Deepwater Horizon offshore oil rig) on 250-meter resolution Red/Green/Blue (RGB) MODIS true color and false color images sourced from the SSEC MODIS Today site (below). Since the oil slick feature was once again located within the sun glint portion of the MODIS image swath, it was very easy to detect on the true color (created using bands 1/4/3 as the R/G/B channels) and false color (created using bands 7/2/1 as the R/G/B channels) imagery.

It appears as though a thin filament of the oil slick has recently been drawn westward (away from the core area of the oil slick near the source), and has been entrained into the sediment outflow region of the Mississippi River. You can follow the changes in appearance of the oil slick on this comparison of MODIS true color image from 21, 25, and 29 April and 01, 04, and 08 May.

MODIS true color (bands 1/4/3) and false color (bands 7/2/1) images

The oil slick appears as a light gray feature on an AWIPS image of the MODIS 0.65 Âµm visible channel data, but shows up as a very warm (darker gray to black enhancement) area on the MODIS 3.7 Âµm “shortwave IR” image due to a high amount of sun glint reflection of solar radiation off the oil slick surface. However, note that the oil slick feature does not exhibit any sort of signature at all on the MODIS 11.0 Âµm “IR window” image (below).

The oil slick was once again a very obvious feature in the 250-meter resolution MODIS true color and false color images on 09 May 2010(above). In this case, note the appearance of the light pink colored pixel near the center of the oil slick on the false color image — the near-IR Band 7 used in that particular RGB image is also sensitive to hot surfaces (for example, due to a fire), which would make such a feature show up as a light pink feature. Indeed, an AWIPS image of the MODIS 3.7 Âµm shortwave IR channel data (below) confirmed the presence of a relatively hot pixel (43.5Âº C, orange color enhancement), which could have been due to a small spot fire that was set in an attempt to burn off some of the surface oil.

MODIS 0.65 Âµm visible and 3.7 Âµm shortwave IR images

===== 10 MAY UPDATE =====

MODIS true color (bands 1/4/3) and false color (bands 7/2/1) images

The oil slick was once again a prominent feature in the 250-meter resolution MODIS true color and false color images on 10 May 2010(above). However, note that the appearance of the oil slick was a bit different than what was seen on the previous days when sun glint was helping to illuminate the feature: on this particular day, the “brighter” portion of the oil slick appeared to be surrounded by a very dark signature. It is not entirely clear what this “dark signature” was on the MODIS true color imagery — but one idea is that it could have been due to oil that was still sub-surface (and had not yet come to the surface where it could then help to reflect light back up toward the satellite in the sun glint region of the overpass swath).

A comparison of the 18:50 UTC 250-meter resolution Aqua MODIS true color Red/Green/Blue (RGB) image — created using MODIS bands 1/4/3 as the R/G/B channels — and the corresponding false color RGB image — created using MODIS bands 7/2/1 as the R/G/B channels — acquired on 04 May 2010 from the SSEC MODIS Today site (above) showed the oil slick from the Deepwater Horizon oil rig explosion and collapse in the northern Gulf of Mexico 14 days earlier. Due to prolonged wind and wave action, the shape and size of the oil slick signature appeared to have changed and spread out in terms of areal coverage (compared to that seen for several days following the accident).

A large explosion aboard the offshore oil rig Deepwater Horizon(located about 52 miles southeast of Venice, Louisiana) occurred around 03 UTC on 21 April 2010. McIDAS images of GOES-13 3.9 Âµm shortwave IR and GOES-13 0.65 Âµm visible channel data (above) showed a “hot spot” (darker black pixels) associated with the large fire during the nighttime hours following the explosion — then the smoke plume could be seen drifting southeastward on the visible imagery with the onset of daylight. The transport of sediment flowing out of the Mississippi River delta region could also be seen on the GOES-13 visible imagery. Note how the initial hot spot (darker black pixels) transitioned to colder values (lighter gray pixels) as pyro-cumulus clouds formed at the top of the rapidly-rising smoke plume.

A 3-image animation of MODIS true color RGB images (below) shows the smoke plume drifting southeastward from the burning oil rig siteÂ on 21 April, followed by a small oil slick on 22 April (thin bright feature meandering eastward from the oil rig site), and finally a much larger oil slick on 25 April (which had grown in size and spread to the north and northeast).

MODIS true color images (21 April, 22 April, and 25 April)

However, it is important to point out that the oil slick feature was easy to detect if it was located within the sun glint portion of the MODIS image swath (where the reflection of solar energy off the thin oil surface makes it appear as a bright feature) — on 25 April, this was the case with the 18:56 UTC overpass of the Aqua satellite. However, about 95 minutes earlier, the oil slick feature was not very apparent on the 17:21 UTC overpass of the Terra satellite, since the sun glint region was located in a different part of the image swath, such that there was no reflection of solar radiation off the oil slick region reaching the satellite at that time (below).

AWIPS images of the MODIS and AVHRR Sea Surface Temperature (SST) products (below) indicated the the SST values within the oil slick feature were often as much as 5Âº to 10Âº F cooler (darker green color enhancement) than the surrounding waters in the northern Gulf of Mexico. The very warm SST values (upper 70s to low 80s F, darker red colors) associated with the Gulf of Mexico Loop Current can be seen in the lower right corner of some of the images.